1. Field of the Invention
The present invention relates to a process for the treatment of wastepaper. More particularly, the present invention relates to a process for de-inking wastepaper. Most particularly, the present invention relates to a process for enhanced removal of ink particles and non-ink contaminants from wastepaper.
2. Description of the Prior Art
In modern times, with the ecological concerns about conservation of raw materials and the rapid decline of available landfill space, it has become increasingly desirable to recover and recycle used raw materials. Thus, recovered wastepaper represents a valuable source of raw material for the paper industry. In order for the wastepaper to be regenerated into a viable starting material and to produce a commercially acceptable paper, the wastepaper must be treated to remove any ink particles and non-ink contaminants.
Wastepaper has long served as a source of the raw fiber materials used in paper-making. Traditionally, fiber from wastepaper was utilized only in the production of low grade paper and paperboard products. Today, however, greater utilization of reclaimed fiber has provided incentive for taking steps to upgrade the reclaimed product These steps include treatment to effectively remove ink from waste fibers in order to permit their use in the manufacture of newsprint and high quality papers. Because of its quantity, waste newsprint is a particularly important feedstock to such reclamation processes.
In the course of the conventional paper reclamation process of interest, de-inking procedures include steps for converting the wastepaper to pulp and contacting the pulp with an alkaline aqueous de-inking medium containing a chemical de-inking agent The physical pulping and the alkalinity of the aqueous medium cause the partial removal of ink from the pulp fiber and the de-inking agent completes this removal and produces a suspension and/or dispersion of the ink particles thus removed from the pulp.
The resulting mixture is subsequently treated by flotation or washing to separate the suspended ink from the pulp.
In most conventional de-inking processes, the wash and/or flotation steps are carried out at an alkaline pH, usually 8.5 to 10.5. Conducting the washing or flotation steps at an alkaline pH is convenient because the fluid carried over from the pulping step is alkaline. In addition, many wash de-inking and flotation de-inking processes use fatty acids as surfactants and these fatty acids are capable of functioning as surfactants only when the aqueous medium is sufficiently alkaline to ionize them.
Typically, reclamation is accomplished in two steps:
1. refining the wastepaper, i.e., fiberizing in water in the presence of the chemicals required for detachment of the printing ink particles, and PA1 2. removal of the detached printing ink particles form the fiber suspension. PA1 a. admixing an alkaline reagent selected from the group consisting of ammonium hydroxide and sodium bicarbonate or mixture thereof with hydrogen peroxide and an aqueous suspension of inked cellulosic fibrous material in amounts whereby said ammonium hydroxide and hydrogen peroxide react at the ink particle/cellulosic fiber interfaces to dislodge said ink particles from said cellulosic materials; and PA1 b. removing said dislodged ink particles from said aqueous suspension.
The second step can be carried out by washing or flotation [Ullmanns Encyclopaedie der technischen Chemie, 4th Edition, Vol.17, pages 570-571(1979)]. In flotation, which utilizes the difference in wettability between printing inks and paper fibers, air is forced or drawn through the fiber suspension. Small air bubbles attach themselves to the printing ink particles and form a froth at the surface of the water which is removed.
The de-inking of wastepaper is normally carried out at alkaline pH values in the presence of alkali metal hydroxides, alkali metal silicates, oxidative bleaches and surfactants at temperatures in the range of from 30.degree. to 50.degree. C. Anionic and/or non-ionic surfactants, for example, soaps, ethoxylated fatty alcohols and/or ethoxylated alkyl phenols, are mainly used as surfactants [Wochenblatt fuer Papierfabrikation, Vol. 17, pages 646-649 (1985)].
Many prior art processes are known for de-inking wastepaper, many of which are directed to the development of de-inking agents. In U.S. Pat. No. 4,586,982 (Poppel etal), there is described a process comprising treating the wastepaper in a pulper at an alkaline pH with alkali silicate, an oxidatively active bleaching agent, an acid selected from the group consisting of fatty acids and resinic acids containing more than ten carbon atoms and a dispersing agent wherein the acid and dispersing agent are employed together in an oil-in-water emulsion.
Additional disclosures of de-inking agents are set forth by, for example, Wood et al in U.S. Pat. No. 4,618,400 (thiol ethoxylate compounds); Wood et al in U.S. Pat. No. 4,561,933 (a mixture of C.sub.8 to C.sub.16 alkanols and alcohol ethoxylates); DeCeuster et al in U.S. Pat. No. 4,343,679 (compounds capable of liberating ions with a positive charge equal or greater than 2); Bridle in U.S. Pat. No. 4,483,742 (pine oil and a soap-making fatty acid); and Tefft in U.S. Pat. No. 4,786,364 (a hydrolyzed copolymer of dimethyidiallyl ammonium chloride and acrylamide).
Other prior art processes are directed to improvements in either washing or flotation methods of separating ink particles from wastepaper fibers.
In U.S. Pat. No. 4,548,673, Nanda et al describe a de-inking flotation method comprising the steps of independently introducing air into a fiber stock slurry, mixing the air bubbles and slurry, and separating the ink-laden air bubbles from the fiber slurry, where each of these steps is independently controlled. In U.S. Pat. No. 4,749,473, Shiori et al describe introducing air bubbles into the wastepaper pulp slurry through a number of orifices formed on a peripheral surface of at least one rotatable horizontal cylinder located in the bottom portion of a flotation vessel. In U.S. Pat. No. 4,277,328, Pfalzer et al describe employing an impeller at the bottom of a flotation apparatus for dispersing air into the wastepaper pulp slurry.
U.S. Pat. Nos. 4,162,186 and 4,518,459 disclose additional methods.
Such methods were reasonably satisfactory and adequate a number of years ago when there was no need to de-ink and reclaim wastepaper having little or no quantities of ground wood. Such papers were printed with standard inks which are more readily removed or saponified with chemicals at elevated temperatures.
In recent years, however, methods of de-inking which involve cooking and the use of chemicals in aqueous media have become increasingly unsatisfactory for a number of reasons. Ink formulations have become more and more complex and involve an increasing use of a wide variety of synthetic resins and plasticizers; with each ink having its own special formulation. Also, increasing amounts of synthetic resins and plasticizers are being used in a wide variety of sizings, coatings, plastic binding adhesives, thermoplastic resins and pressure sensitive label adhesives. Furthermore, the use of multi-colored printing and multi-colored advertisements have become increasingly popular in recent years and these involve a wide variety of new ink formulations. Many of the new ink formulations incorporate new pigments, dyesand toners which are difficult to remove by conventional aqueous de-inking chemicals. The former methods of de-inking and reclaiming wastepaper by chemical and cooking techniques are not adapted for, or adequate for, removing the new types of inks and coating resins. Due to high contents of thermoplastic resins, the softening action of heat and chemicals alone makes their separation from the fibers very difficult Additionally, the action of heat and chemicals tends to irreversibly set and more firmly bond some of the present day pigments to the fibers and fix dyes and toners to the fibers through staining.
The challenges that the pulp and paper industry is trying to meet today in the recycling area are to (1) economically produce quality paper meeting the consumer demands and also the legislative demands for the content of recycled paper; and (2) increase the process efficiency in order to make use of recovered paper which currently cannot be processed economically. Currently, most recycling processes are geared only to use high quality recovered paper costing over $150 per ton. Such material is limited in quantity and is in high demand due to the regulations governing the incorporation of certain percentages of recycled fiber in many paper commodities. There exists a need for new recycling processes which are more economical and can handle a wider range of recovered paper. One of the most important steps in recycling the recovered paper is that of de-inking. There also exists a need for methods of de-inking that can handle (1) a wider variety of printed material (newsprint to high quality glossy magazine paper) and (2) a higher pulp density than the conventional processes.
For the above and other reasons, conventional de-inking techniques used in reclaiming processes for wastepaper are no longer efficient or effective for many current needs.
The need for a satisfactory de-inking process has become increasingly important due to greatly expanded utilization of paper and difficulty in disposal of the old papers due to projected lack of landfill sites.
In this regard, to preserve natural resources and minimize environmental problems, the need for developing useful and efficient paper recycling processes becomes of critical importance.